The present invention generally relates to optoelectronic communication systems. More particularly, the present invention relates to a method for encapsulating optoelectronic devices for optical coupling.
Plastic encapsulation of optoelectronic devices may provide cost effective and reliable packaging schemes which otherwise may be more complicated, expensive and bulky. These packaging schemes, referred to as optical subassemblies (OSAs), are the mechanisms that enable the accurate positioning of optical fibers to provide for efficient optical coupling between optical fibers and optoelectronic devices such as VCSELs (vertical cavity surface emitting lasers), other lasers or photodetector devices.
A limitation associated with conventional encapsulation processes and designs, however, is that the precision of the conventional encapsulation processes is inadequate for many VCSEL and photodetector applications, specifically those which require high coupling efficiencies, dense packaging, high speed devices or a thin gap between the optoelectronic device and the optical fiber to which it is coupled. Conventional techniques are often not adequately precise because, using conventional technology, it is not possible to form the encapsulant by directly referencing the encapsulation molds to the optoelectronic devices themselves; rather, the encapsulation molds indirectly reference the devices through the lead frames or other media upon which the optoelectronic device is mounted. Therefore, using traditional encapsulation processes, even if the encapsulation mold references the lead frame perfectly, the variabilities of the lead frame itself, the alignment of the optoelectronic device to the lead frame, the variability in the die attach epoxy junction and the thickness variability of the optoelectronic device, may render it inherently difficult to achieve micron scale tolerances when shaping and positioning the encapsulant.
In optoelectronic coupling, an attractive optical train, especially for high-end optoelectronic devices such as VCSELs and P-i-N photodetectors that require high coupling efficiencies, is an optical train with the fewest variables. This may generally be achieved by directly xe2x80x9cbutt-couplingxe2x80x9d the optoelectronic device to the optical fiber or other optical transmission medium. This is true for xe2x80x9cpig-tailedxe2x80x9d applications in which a section of the optical fiber is permanently attached to the OSA, or for xe2x80x9cconnectorizedxe2x80x9d applications where the optical fiber may be plugged into the OSA by utilizing industry standardized optical fiber connectors. When butt-coupling techniques are used to directly couple the optical fiber to an encapsulated optoelectronic device, the encapsulant typically must be precisely and accurately positioned over the optoelectronic device, in order to maximize optical coupling efficiency. Because of the above-described limitations, however, the plastic encapsulation of optoelectronic devices which are to be butt-coupled to optical fibers, is not practical using conventional encapsulation processes. As such, optoelectronic design engineers have been forced down alternate paths such as including lenses and hermetic TO cans, when coupling optoelectronic devices to optical fibers. The alternate arrangements may add variables to the optical train and are more costly and difficult to produce.
The present invention provides an apparatus and method for encapsulating an optoelectronic device on a substrate. In an exemplary embodiment, the encapsulant is formed over the optoelectronic device by forming an fluid encapsulant material over the optoelectronic device, then referencing the optoelectronic device or the optoelectronic device die during an alignment process used to shape the fluid encapsulant material into a shaped encapsulant. The shaped encapsulant may then be cured or otherwise hardened to form an appropriately solid shape. The encapsulant may be shaped to mate with a corresponding end face of an optical transmission medium. In another embodiment, the present invention further provides for directly butt-coupling an optoelectronic transmission medium to the encapsulated optoelectronic device to produce a butt-coupled connection with a high optical coupling efficiency. The butt-coupled connection is applicable to both pig-tailed and connectorized arrangements.